Set up your PC to share the drive. On the Mac use Finder menu Go->Connect to server, enter smb://ip.address.of.thepc/sharenameofyourdrive and click OK. Enter your username/password for the PC if that's how the sharing is set up and it should show up as an icon on your desktop. Double-click that icon and you'll see your files. Drag them to where you want them to go on your Mac. Wait. [Profit?] Depending on the speed of your internal network and how much stuff you're copying it might take a little while.

ip.address.of.thepc would, of course be something like 192.168.1.X where X is whatever the number assigned by your router (if you have a router; you have a router don't you? You should get one if you don't.) In a command window on the PC use the command ipconfig to find out what IP address has been assigned.